Provisioning of emergency services in a voice-over-packet environment

ABSTRACT

The delivery of emergency services to users of a set of communication devices in a packet-switched network is enabled by a method that determines a routing key corresponding to a particular directory number that is associated with a particular communication device, and stores the directory number and the corresponding routing key in a database accessible to a packet switch. The steps of determining and storing are executed during a provisioning phase, in the absence of an emergency call placed by the communication device. The routing key is indicative of routing instructions to be followed by the packet switch upon receipt of a future emergency call placed by the communication device. When the call is received by the packet switch, it will consult the database to obtain the routing key associated with the directory number and send the call as well as the routing key over a path dedicated to emergency calls.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit under 35 U.S.C. 119(e) ofProvisional U.S. Patent Application Ser. No. 60/617,656, to WilliamCrago et al., filed on Oct. 13, 2004, hereby incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention relates to the field of telecommunications ingeneral and, more specifically, to the delivery of emergency services tousers of communication devices in a network that providesvoice-over-packet services.

BACKGROUND

The current Emergency Services Enhanced 9-1-1 (E911) infrastructure inNorth America is based on a distribution of Primary Public SafetyAnswering Points (P-PSAPS, hereinafter referred to solely as PSAPs)accessible from the Public Switched Telephone Network (PSTN) via aspecial group of telephone lines dedicated solely to emergency use. Thesame applies to other emergency codes used in other parts of the world,e.g., E112 in continental Europe, E999 in England, etc.

In the current infrastructure, each individual telephone number isassigned a corresponding PSAP that is nearest to the physical locationof the user of that telephone number. The physical location of the useris assessed on the basis of the area code and local exchange of thetelephone number. When a user places an emergency call, the callingpartys telephone number is transmitted with the call, and on the basisof the originating telephone number, the emergency call will be routedto the designated PSAP along one of the dedicated emergency lines. Uponreceipt at the PSAP, the call is answered by a trained responder. Byvirtue of an automatic location identification (ALI) database which mapseach telephone number to an address, the responder is able to obtain thephysical location of the calling party and dispatch a police officer,firefighter or ambulance as necessary.

With the advent of the Internet, society has witnessed the expansion ofa global packet-switched network into an ever increasing number of homesand businesses. This has put ever increasing numbers of users intocontact with one another, usually at little cost for unlimited use.Meanwhile, advances have been made in delivering voice communicationover packet networks, driven primarily by the cost advantage of placinglong-distance calls over the Internet as opposed to the leased lines ofthe worlds telcos. Technology dealing with the delivery of real-timevoice calls over a packet-switched network is generally known asvoice-over-packet or voice-over-Internet-Protocol (voice-over-IP), andoften simply referred to as “VoIP”.

From a purely technological standpoint, the successful deployment ofVoIP has several challenges, typically related to latency andcongestion. Still, despite these and other technical drawbacks, manyconsumers have opted to subscribe to VoIP services, motivated bysignificant cost savings in the area of long-distance calling. This hasled to a trend, whereby some residential and business consumers haveactually chosen to abandon their “basic” PSTN connection in favour of aVoIP connection, not only to satisfy their long distance requirementsbut also to conduct local, day-to-day telephony. One area where thisshift to all-VoIP paradigm can be problematic for consumers (and VoIPservice providers) is in the delivery of emergency services.

Specifically, the call delivery technology is fundamentally differentfor VoIP, and as a result, the dialing of 9-1-1 during a VoIP connectiondoes not work today in the same way as for a basic PSTN connection. Forexample, VoIP users can select their own telephone numbers, which maycomprise an “area code” and a “local exchange” that are unrelated to thephysical location from which calls will be placed. If the VoIP userdials 9-1-1, the call may be directed to a PSAP located in a differentpart of the country, significantly reducing the value of the emergencyservices being provided.

Recognizing these defects, some VoIP service providers have enhancedtheir offerings in the area of emergency services. For example, thereare consumer VoIP solutions which allow the transfer of a 9-1-1 callfrom the VoIP network to the nearest PSAP in accordance with level i1 ofthe service levels proposed by the National Emergency Number Association(NENA) and the Voice over the Net (VON) coalition.

However, in accordance with this and other i1-compliant solutions,emergency calls are not delivered via the dedicated emergency lines andtrunks described above, but instead arrive at the nearest PSAP via thePSAP's ordinary, i.e., administrative, lines. Since many PSAPs areunprepared to handle calls over ordinary telephone lines, this creates avariety of problems, ranging from the low priority typically given toadministrative calls, to the possibility of having an emergency callanswered by improperly trained staff such as a receptionist or, worsestill, by an auto-attendant during off-normal hours.

Against this background, it is clear that further improvements areneeded in the delivery of emergency services to persons dialing 9-1-1from a VoIP-enabled telephone or device.

SUMMARY OF THE INVENTION

A first broad aspect of the present invention seeks to provide a methodof enabling the delivery of emergency services to users of a set ofcommunication devices in a packet-switched network, each of thecommunication devices being associated with a respective directorynumber. The method comprises determining a routing key corresponding toa particular directory number that is associated with a particularcommunication device, and storing the particular directory number andthe corresponding routing key in a database accessible to a packetswitch in the packet-switched network. The steps of determining andstoring are executed in the absence of an emergency call placed by theparticular communication device.

A second broad aspect of the present invention seeks to provide a methodof enabling the delivery of emergency services to users of a set ofcommunication devices in a packet-switched network, each of thecommunication devices being associated with a respective directorynumber. The method comprises determining a routing key corresponding toa particular directory number that is associated with a particularcommunication device, and storing the particular directory number andthe corresponding routing key in a database local to a packet switch inthe packet-switched network.

A third broad aspect of the present invention seeks to provide a methodof enabling the delivery of emergency services to users of a set ofcommunication devices in a packet-switched network, each of thecommunication devices being associated with a respective directorynumber. The method comprises determining the identity of an emergencyzone corresponding to a particular directory number that is associatedwith a particular communication device, and providing the particulardirectory number and the identity of the corresponding emergency zone toa packet switch in the packet-switched network. At the packet switch,and on the basis of the identity of the corresponding emergency zone, arouting key corresponding to the particular directory number isdetermined.

A fourth broad aspect of the present invention seeks to provide a methodof enabling the delivery of emergency services to users of a set ofcommunication devices in a packet-switched network, each of thecommunication devices being associated with a respective directorynumber. The method comprises determining a routing key corresponding toa particular directory number that is associated with a particularcommunication device, and storing the particular directory number andthe routing key corresponding to the particular directory number in adatabase accessible to a packet switch in the packet-switched network.The routing key corresponding to the particular directory number isindicative of routing instructions to be followed by the packet switchupon receipt of a future emergency call placed by the particularcommunication device.

Other broad aspects of the present invention seek to provide computerreadable storage media containing a program element for execution by acomputing device to implement one or more of the above methods.

According to yet another broad aspect, the present invention seeks toprovide a registration entity for enabling the delivery of emergencyservices to users of a set of communication devices in a packet-switchednetwork, each of the communication devices being associated with arespective directory number. The registration entity comprises a controlentity and an I/O for communicating with a packet switch in thepacket-switched network. The control entity is operative to execute thesteps of determining a routing key corresponding to a particulardirectory number that is associated with a particular communicationdevice, and storing the particular directory number and the routing keycorresponding to the particular directory number in a databaseaccessible to the packet switch. The steps of determining and storingare executed for the particular communication device in the absence ofan emergency call placed by the particular communication device.

According to still another broad aspect, the present invention seeks toprovide a network entity for enabling the delivery of emergency servicesto users of a set of communication devices in a packet-switched network,each of the communication devices being associated with a respectivedirectory number. The network entity comprises a control entity and anI/O in communication with the control entity. The control entity isoperative to execute the steps of determining a routing keycorresponding to a particular directory number that is associated with aparticular communication device, and storing the particular directorynumber and the corresponding routing key in a database local to a packetswitch in the packet-switched network.

According to another broad aspect, the present invention seeks toprovide a packet switch for enabling the delivery of emergency servicesto users of a set of communication devices in a packet-switched network,each of the communication devices being associated with a respectivedirectory number. The packet switch comprises a control entity and anI/O in communication with the control entity. The control entity isoperative to execute the steps of determining a routing keycorresponding to a particular directory number that is associated with aparticular communication device, and storing the particular directorynumber and the routing key corresponding to the particular directorynumber in a database. The routing key corresponding to the particulardirectory number is indicative of routing instructions to be followed bythe packet switch upon receipt of a future emergency call placed by theparticular communication device.

According to yet another broad aspect, the present invention seeks toprovide a computer-readable storage medium for storing data for accessby an application program being executed at a packet switch in apacket-switched network. The memory comprises a plurality of records,each record identifying a directory number associated with a respectivecommunication device in the packet-switched network, and a routing keycorresponding to the directory number. The routing key corresponding toa particular directory number is indicative of routing instructions tobe followed by the packet switch upon receipt of a future emergency callplaced by the communication device associated with the particulardirectory number.

These and other aspects and features of the present invention will nowbecome apparent to those of ordinary skill in the art upon review of thefollowing description of specific embodiments of the invention inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C show in schematic form, various embodiments of anarchitecture of network elements suitable for the delivery of emergencyservices;

FIGS. 2A to 2J show interaction of the various network elements in thearchitecture of FIG. 1A during a provisioning phase;

FIGS. 3A and 3B conceptually illustrate the contents of a tablemaintained by a network element forming part of the architecture of FIG.1, in accordance with two specific embodiments of the present invention;

FIGS. 4A to 4F show interaction of the various network elements in thearchitecture of FIG. 1A during a call handling phase.

DETAILED DESCRIPTION OF THE EMBODIMENTS

With reference to FIG. 1A, there is shown a network element architecturesuitable for the delivery of emergency services in accordance with anembodiment of the present invention. A packet-switched network 100,which may or may not be the public Internet, comprises a backbone towhich users have access via customer premises equipment 102 such as amodem 104 in combination with a residential gateway 106. In someembodiments, the modem 104 and the residential gateway 106 may becombined into a single unit at the customer premises.

A VoIP customer desirous of obtaining telephony services via thepacket-switched network 100 may be provided with a special-purpose VoIPtelephone or device that connects directly to the residential gateway106. In another embodiment, and as illustrated in FIG. 1A, the VoIPcustomer utilizes a conventional analog telephone 110 which connects tothe residential gateway 106 using an analog terminal adapter (ATA) 112.The ATA 112 permits the VoIP customer to re-use conventional telephonyhardware in a VoIP environment, thus obviating the need to purchase andmaintain a second telephone strictly for IP telephony purposes.Generally speaking, however, it is immaterial to the present inventionwhether the VoIP customer uses a special-purpose VoIP telephone or aconventional analog telephone 110 coupled to an ATA 112.

In a typical residential application, the packet-switched network 100 isaccessed by the modem 104 in the customer premises equipment 102 uponestablishing a connection to a modem 108 belonging to a network serviceprovider, commonly an Internet service provider (ISP). The connection ismade via an access infrastructure, examples of which include but are notlimited to copper telephone lines (for an ADSL modem) 104 and coax cable(for a cable modem 104). It should be further understood that thepresent invention applies to the delivery of emergency services not onlyin a residential context but in other contexts such as business andcorporate applications, where access to the packet-switched network 100may be provided by a server that in some cases is directly connected tothe packet-switched network 100.

A VoIP service provider maintains a registration entity 190, which VoIPcustomers may access via the packet network 100. In a non-limitingexample of implementation, the registration entity 190 may be embodiedas a server having a control entity and an I/O. Initially, potentialVoIP customers contact the VoIP service provider via the registrationentity 190. A given VoIP customer registers with the registration entity190 and obtains a VoIP telephone number N (hereinafter referred to as a“directory number”). The VoIP customer, identified by the directorynumber N, can then begin to place calls into (and receive calls from)the packet-switched network 100. The registration entity 190 performsvarious other functions which will be described in further detail lateron.

At the edge of the packet-switched network 100 there is provided anetwork element 114, which may be referred to as a packet switch orsoftswitch, and which comprises suitable circuitry, software and/orcontrol logic for providing various communication services to VoIPcustomers. Examples of such communication services include but are notlimited to call waiting, call forwarding, and so on. In addition, thenetwork element 114 comprises suitable circuitry, software and/orcontrol logic for exchanging calls with entities outside thepacket-switched network 100. Where a call is placed by a VoIP customer,there are at least two circumstances that require the call to passthrough the network element 114, namely, (i) a call placed to atelephone number that is reachable only via the Public SwitchedTelephone Network (PSTN) 116 and (ii) an emergency call.

In the former case, the network element 114 detects when a VoIP customerin the packet-switched network 100 is attempting to reach a destinationthat can only be reached via the PSTN 116, in which case the call isrouted via a network 124 to one of a plurality of gateways 118A, 118Bthat connect to the PSTN 116.

In the latter case, the network element 114 detects when a VoIP customerin the packet-switched network 100 has dialed (either explicitly or viaa speed dial function or in some other way) an emergency number such as“9-1-1”. In such a case, the call, hereinafter referred to as anemergency call, is routed to one of the gateways 118A, 118B, whichconnect not only to the PSTN 116 as described above, but also to anetwork of dedicated emergency lines and Public Safety Answering Points(PSAPs), hereinafter collectively referred to as an E911 network 122.

In addition to the above, when handling an emergency call, the networkelement 114 comprises circuitry, software and/or control logic suitablefor outpulsing a “routing key” associated with the directory number ofthe VoIP customer having placed the emergency call. The routing keyaccompanies the emergency call as it is routed by the network element114 to the appropriate one of the gateways 118A, 118B. Further detailregarding routing keys and the operation of the network element 114 willbe given later on in this description.

In a specific example of implementation, the network element 114 is theMultimedia Communication Server 5200 from Nortel Networks Limited,Brampton, Ontario, Canada, although it should be understood that thepresent invention applies equally to other makes, models and types ofpacket switches or softswitches that have (or can be configured to have)the ability to assign a routing key to a VoIP customers directorynumber.

As previously mentioned, the network element 114 is connected to thegateways 118A, 118B via the network 124. In some embodiments, thenetwork 124 may be part of the packet-switched network 100 while inother embodiments it may not. In still other embodiments, rather thanbeing connected via the network 124, the network element 114 may beconnected to each gateway 118A, 118B by a respective communication linkthat can be optical fiber, coaxial cable, wireless, free-space optical,etc. It is noted that the network 124 (or the communication link(s), asthe case may be) carries multiple telephone calls simultaneously. In anembodiment of the present invention, emergency calls are treateddifferently from non-emergency calls and therefore it is envisaged thatdistinct virtual trunk groups will be established for either type ofcall (non-emergency and emergency), as well as for each of the gateways118A, 118B.

In addition to communicating with the network element 114 via thenetwork 124, the gateways 118A, 118B in FIG. 1A also communicate withcomponents of the PSTN 116 and the E911 network 122. Specifically,gateway 118A is connected to the PSTN 116 via a plurality ofhigh-capacity switches 128A, 128B and is also connected to the E911network 122 via a plurality of high-capacity switches 132A, 132B.Similarly, gateway 118B is connected to the PSTN 116 via a plurality ofhigh-capacity switches 148A, 148B and is also connected to the E911network 122 via a plurality of high-capacity switches 152A, 152B. Itshould be understood that the specific architecture shown in FIG. 1A ismerely for purposes of illustration; in other architectures that arewithin the scope of the present invention, there may be more or fewergateways, and not all gateways need be connected to both the PSTN 116and the E911 network 122.

In a specific example of implementation, each or either of the gateways118A, 118B may be embodied as the Communication Server 2000 from NortelNetworks Limited, Brampton, Ontario, Canada, although it should beunderstood that the present invention applies equally to other makes,models and types of gateways.

An example of a basic function of the gateways 118A, 118B is to allownon-emergency calls originated in the packet-switched network 100 to becompleted via the PSTN 116 (which is circuit-switched) and vice versa.Another example of a basic function of the gateways 118A, 118B is totake emergency calls originated in the packet-switched network 100 andto route them into the E911 network 122, which is circuit-switched (muchlike the PSTN 116).

Continuing with the description of the architecture in FIG. 1A, switch132A is connected via a first portion of the E911 network 122 to a firstplurality of PSAPs, including PSAP 138A and PSAP 138B, while switch 132Bis connected via a second portion of the E911 network 122 to a secondplurality of PSAPs, including PSAP 138C and PSAP 138D. Similarly, switch152A is connected via a third portion of the E911 network 122 to a thirdplurality of PSAPs, including PSAP 138E and PSAP 138F, while switch 152Bis connected via a fourth portion of the E911 network 122 to a fourthplurality of PSAPs, including PSAP 138G and PSAP 138H. Of course, thisdistribution of PSAPs is not to be considered as limiting.

Each switch routes a received call in accordance with a connection map.For an emergency call received at a given one of the switches 132A,132B, 152A and 152B, the call will specify a desired PSAP to be reached.The identity of the desired PSAP may be expressed in the form of a “E911telephone number”. Thus, for example, switch 132B will recognize anemergency call that has an associated “E911 telephone number” whichspecifies either PSAP 138C or PSAP 138D, and will route the emergencycall accordingly. The E911 telephone number of may correspond to thetelephone number of a specific PSAP along a dedicated in the E911network 122, and is usually held confidential by the local exchangecarrier.

In addition, switches 132A, 132B, 152A and 152B may have a furtherability to forward an emergency call towards a specialized entity otherthan the PSAPs shown in the drawings. The desirability of doing soarises when a trained responder at a PSAP determines that a specialagency (e.g., police, fire or ambulance) may need to be contacted.Forwarding of the emergency call may be done in accordance with aforwarding table that maps plural emergency telephone numbers to eachdirectory 11 number. Each emergency telephone number mapped to a givendirectory number is associated with a respective forwarding code thatsignifies either “police”, “fire” or “ambulance”. During an actual callreceived at a PSAP, a particular forwarding code would be applied by atrained responder at the PSAP in question and sent to switch 132B. Uponreceipt of the particular forwarding code, switch 132B is operative tolook up the directory number of the call in question and to forward theemergency call towards the appropriate agency using the emergencytelephone number for the forwarding code in question. In practice, thetrained responder may enter into a three-way conference before the callforward is complete.

It has already been mentioned that PSTN calls and emergency calls arereceived from the network 124 over different virtual trunk groups. Thismakes it a simple task for a particular one of the gateways 118A, 118Bto determine towards which network (i.e., the PSTN 116 or the E911network 122) to direct a given call. However, in the case of anemergency call received by, say, gateway 118A, there is still a questionof whether to route the call towards switch 132A or towards switch 132B.To this end, gateway 118A maintains a connection map 134A whichassociates each potential received routing key with one of the switches,either switch 132A or switch 132B. In addition, gateway 118A may convertthe routing key into a format more understandable to the switches 132A,132B. One example of a more understandable format is the “E911 telephonenumber” format mentioned above. The E911 telephone number accompaniesthe emergency call as it is routed by the gateway 118A to theappropriate one of the switches 132A, 132B.

In an analogous fashion, gateway 118B maintains a connection map 134Band also may convert received routing keys into E911 telephone numbers.Further detail regarding E911 telephone numbers and the operation of thegateways 118A, 118B will be given later on in this description.

Switches 132A, 132B, 152A and 152B currently operate entirely within thecircuit-switched domain. However, this does not rule out the possibilityof the switches 132A, 132B, 152A and 152B being retrofitted with thefunctionality of an IP gateway that would allow an IP connection fromthe network element 114 directly to the switches 132A, 132B, 152A and152B via dedicated virtual trunk groups, thus bypassing the need forgateways 118A and 118B in this intermediate position. This possibilityis envisaged in FIG. 1C. It is noted that a set of gateways 198A, 198Bis still used to connect the network element 114 to the legacy switches128A, 128B, 148A, 148B leading to the PSTN 116.

Returning to FIG. 1A, the PSAPs 138A to 138H are connected to an ALIdatabase 140. The ALI database 140 is a known database that storesstreet addresses and associated telephone numbers, thus enabling a PSAPoperator to obtain the street address corresponding to a given directorynumber from which an emergency call has originated. The ALI database 140is connected to a 9-1-1 database management system (9-1-1 DBMS) 150,which maintains a mapping of street addresses to “emergency zones”, suchas a municipality, county or district, for example. The 9-1-1 DBMS 150is accessible to the registration entity 190, either by a direct link orvia the packet-switched network 100.

The architecture in FIG. 1A also comprises a street address guide (SAG)160, which is accessed by the registration entity 190, either by adirect link or via the packet-switched network 100. The street addressguide 160 provides validation of a street address in order to determinewhether a particular entry corresponds to a realistic address.

In accordance with an embodiment of the present invention, certain stepsare performed for each VoIP customer during a provisioning phase, whichoccurs before the placement of an emergency call by that VoIP customer,and is now described with reference to the signal flow diagrams in FIGS.2A through 2H, which correspond to steps 2-A through 2-H. In fact, itmay be advantageous to perform the following steps during the samegeneral time frame as when the VoIP customer obtains his or herdirectory number N.

At step 2-A, the VoIP customer provides a service address to theregistration entity 190. The service address, which may differ from thebilling address, is typically the geographic location of the VoIPcustomer, which may be the civic (street) address where the VoIPcustomer is located, although it is envisaged that in some embodimentsit may be the latitude/longitude of the VoIP customer or some other formof localization data. The manner in which the VoIP customer provides theservice address to the registration entity 190 is not material to thepresent invention and may include the usage of the web, email, snailmail, etc. It is noted that step 2-A may be performed at the same timeas when the VoIP customer is first assigned a directory number N and infact it is envisaged that the execution of step 2-A may even be made acondition for the delivery of VoIP services.

At step 2-B, the registration entity 190 validates the service addresssupplied by the user. This can be achieved by running the serviceaddress through a street address guide (SAG) 160 that is available tothe VoIP service provider. Validation provides an assurance that theservice address given by the user is a valid address, i.e., reallyexists, and therefore will be capable of being meaningfully associatedwith an emergency zone and its designated PSAP. If validation at step2-B is unsuccessful, then the VoIP customer may be asked to re-enter theservice address with a greater degree of precision or may be prompted toresolve an ambiguity by choosing the service address from a list of twoor more address choices. Step 2-B may also be performed interactivelywith the VoIP customer and may involve the intervention of a customerservice representative.

Provided validation at step 2-B is successful, the registration entity190 proceeds to step 2-C, which consists of supplying the validatedstreet address to the 9-1-1 DBMS 150. The 9-1-1 DBMS 150 has thefunctionality of identifying an emergency zone associated with theservice address. In one embodiment, the 9-1-1 DBMS 150 maintains amapping that associates postal codes (zip codes) to emergency zones.Thus, a given service address having a given postal code will map to acorresponding emergency zone.

At step 2-D, the 9-1-1 DBMS 150 returns a file processing confirmation209 to the registration entity 190. The file processing confirmation 209may identify the emergency zone (hereinafter denoted 210) associatedwith the service address in question.

At step 2-E, which may actually be executed before step 2-D, the 9-1-1DBMS 150 provides the directory number N and the validated streetaddress to the ALI database 140 for storage therein.

At step 2-F, the 9-1-1 DBMS 150 updates the forwarding tables at theswitches 132A, 132B, 152A, 152B, with routing information 202 for thepurposes of eventual call transfer to dispatch agencies (police, fire,ambulance) as per established routines. In an example, the individualemergency telephone numbers corresponding to police, fire and ambulanceagencies which are associated with emergency zone 210 are entered intothe forwarding table in association with directory number N.

At step 2-G, which may actually be executed before step 2-F, theregistration entity 190 consults a call routing list (CRL) 188, whichassociates emergency zones 210 to individual “routing keys” 214. Theresult of step 2-G is the obtaining of a routing key 214 thatcorresponds to the emergency zone 210. By virtue of the associationbetween each directory number N and its emergency zone 210, and byvirtue of the association between each emergency zone 210 and itsrouting key 214, it will be apparent that each directory number N willbe associated with a routing key 214. Also, since more than oneemergency zone may be serviced by the same PSAP, a plurality ofdirectory numbers N will share the same routing key 214.

At step 2-H, the registration entity 190 provides the directory number Nand the associated routing key 214 (obtained at step 2-G) to the networkentity 114. The network entity 114 enters this information into a table178 local to the network entity 114. The table 178 may be stored in thenetwork entity 114 or otherwise directly accessible thereto.

FIG. 3A shows a specific, non-limiting example of the table 178 that islocal to the network entity 114. Basically, the table 178 comprises aplurality of records 204, each containing a directory number N and arelated routing key 214. A particular routing key 214 comprisesinformation that defines a route to be taken by an emergency call inorder to reach a particular PSAP. In one embodiment, not to beconsidered as limiting, the routing key 214 comprises a gatewayidentifier 214A and a routing code 214B. Further detail regarding thepurpose and effect of fields 214A, 214B will be given later on in thisspecification.

In an alternative embodiment of steps 2-G and 2-H, shown in FIGS. 2-Iand 2-J, the registration entity 190 provides the directory number N andthe associated emergency zone 210 to the network entity 114, and it isthe network entity 114 that consults a call routing list (CRL) 188 inorder to obtain the appropriate routing key 214 for the emergency zone210 in question. In this case, and with reference to FIG. 3B, the table178′ local to the network element 114 would comprise a plurality ofrecords, each containing a directory number N, a related emergency zone210 and a related routing key 214.

With additional reference now to the diagrams of FIGS. 4-A to 4-F,placement of an emergency call and operation of the various elements inthe architecture of FIG. 1 in a “call handling” phase is now described.

At step 4-A, the network element 114 detects an emergency call 400received from a VoIP customer associated with a particular directorynumber N.

At step 4-B, the network element 114 consults the table 178 (or 178′)which is local to the network element 114 and retrieves the routing key214 for the directory number N. As previously mentioned, the routing key214 contains a gateway identifier 214A, which identifies the destinationgateway towards which the emergency call 400 should be routed. Let thisdestination gateway be gateway 118A. In addition, the routing key 214contains a routing code 214B which, when interpreted by gateway 118A,will identify (i) a destination switch towards which gateway 118A shouldroute the emergency call 400 and (ii) the destination PSAP for theemergency call 400. For the purposes of this example, let thedestination switch be switch 132B and let the destination PSAP be PSAP138C.

At step 4-C, the network element 114 routes the emergency call 400 ontothe virtual trunk group assigned to the destination gateway, in thiscase gateway 118A. In addition, as part of step 4-C, the network element114 forwards the routing code 213B along with the emergency call 400. Inan alternative embodiment, the network element 114 forwards the routingkey 214 in its entirety. The forwarded information accompanies theemergency call 400 as it is routed to gateway 118A.

At step 4-D, the gateway 118A receives the emergency call 400 from thenetwork element 114. The emergency call 400 is accompanied by at leastthe routing code 214B. Gateway 118A reads the routing code 214B in orderto learn (i) the identity of the destination switch (in this case switch132B) towards which the emergency call 400 should be routed by gateway118A and (ii) the identity of the destination PSAP (in this case PSAP132C) towards which the emergency call 400 should be routed by thedestination switch 132B. Additionally, gateway 118A obtains the E911telephone number corresponding to the destination PSAP 138C, hereinafterdenoted 250. The destination gateway 118A then proceeds to route theemergency call 400 to the destination switch 132B and forwards the E911telephone number 250 along with the emergency call 400.

At step 4-E, the destination switch (in this case switch 132B) routesthe received emergency call 400. Routing is performed on the basis ofthe E911 telephone number 250 received from gateway 118A, resulting inthe emergency call 400 being transferred onto a dedicated line leadingtowards the destination PSAP (in this case PSAP 138C) over the E911network 122.

At step 4-F, once the incoming emergency call 400 is received at thedestination PSAP 138C, it is handled by a trained responder. Withknowledge of the directory number N (which follows the emergency call400 from its inception), the responder obtains the validated serviceaddress associated with the directory number N. In one embodiment, theresponder queries the ALI database 140 upon receipt of the emergencycall 400 in order to obtain the validated service address. In analternative embodiment, the validated service address is pushed by theALI database 140 during a previous step. Specifically, after step 4-Edescribed above, receipt of the emergency call 400 by switch 132B couldbe followed by switch 132B supplying the directory number N to the ALIdatabase 140, which then pushes the validated service address to thedestination PSAP 138C. In either case, the responder learns the exactgeographic location of the caller and can dispatch emergency personnelif necessary.

In an example scenario, the responder may determine that a particulartype of emergency agency (police, ambulance, fire) needs to bedispatched. A forwarding code can be dialed back to switch 132B fromwhich the emergency call 400 originated. The forwarding code triggersswitch 132B to use its internal forwarding table in order to forward theemergency call 400 to a particular emergency telephone number where theappropriate agency can be reached. Since the updating of the forwardingtable was done in the provisioning phase at step 2-F (as describedearlier), the emergency call 400 will be automatically forwarded to theagency of the appropriate type that is geographically in the bestposition to handle the emergency call 400.

Of course other embodiments of explicit routing using a routing key 214are within the scope of the present invention. For instance, it isenvisaged that the routing code 214B mentioned above may comprise onlythe E911 telephone number 250 corresponding to the destination PSAP. Insuch a scenario, a gateway that receives the emergency call and theassociated E911 telephone number 250 would access a local table toobtain the identity of the switch that is connected to the destinationPSAP. In fact, the functionality of consulting a local table could berelegated to network element 114, such that it is the network element114 that determines the ports that need to be used by the gateway whenrouting the emergency call in question, in order that the call reach thedestination PSAP. FIG. 1B shows such an embodiment, where the connectionmaps (134A, 134B in FIG. 1A, formerly executed by the gateways 118A,118B, respectively) have been consolidated into a single connection mapexecuted at the network element 114.

From the above description, it will be noted that the assignment of arouting key 214 to each directory number N permits independence of thedirectory number N and the destination PSAP. In other words, there neednot be any relationship between the “area code” or “local exchange” ofthe directory number N and the destination PSAP, which is unlike thecase with the traditional telephony infrastructure. As a result, VoIPservice providers can assign arbitrary directory numbers to theircustomers, while ensuring that emergency services will be dispatchedeffectively by the appropriate PSAP for each customer. Moreover, as hasbeen shown using the example of FIGS. 4-A to 4-F, emergency calls 400can be directed to the appropriate PSAP over a dedicated emergencycircuit in the E911 network 122, rather than over an administrativeline, thereby maximally assuring a prompt response by trained personnel.

Those skilled in the art will appreciate that in some embodiments, thefunctionality of parts of the network element 114 and/or theregistration entity 190 may be implemented as pre-programmed hardware orfirmware elements (e.g., application specific integrated circuits(ASICs), electrically erasable programmable read-only memories(EEPROMs), etc.), or other related components. In other embodiments,parts of the network element 114 and/or the registration entity 190 maybe implemented as an arithmetic and logic unit (ALU) having access to acode memory (not shown) which stores program instructions for theoperation of the ALU. The program instructions could be stored on amedium which is fixed, tangible and readable directly by the networkelement 114 and/or the registration entity 190, (e.g., removablediskette, CD-ROM, ROM, or fixed disk), or the program instructions couldbe stored remotely but transmittable to the network element 114 and/orthe registration entity 190 via a modem or other interface device (e.g.,a communications adapter) connected to a network over a transmissionmedium. The transmission medium may be either a tangible medium (e.g.,optical or analog communications lines) or a medium implemented usingwireless techniques (e.g., microwave, infrared or other transmissionschemes).

While specific embodiments of the present invention have been describedand illustrated, it will be apparent to those skilled in the art thatnumerous modifications and variations can be made without departing fromthe scope of the invention as defined in the appended claims.

1. A method of enabling the delivery of emergency services to users of aset of communication devices in a packet-switched network, each of thecommunication devices being associated with a respective directorynumber, the method comprising: determining a routing key correspondingto a particular directory number that is associated with a particularcommunication device; and storing the particular directory number andthe corresponding routing key in a database accessible to a packetswitch in the packet-switched network, wherein the packet switch isconnected to a plurality of public safety answering points (PSAPs) via adedicated emergency network and wherein the routing key corresponding tothe particular directory number defines a route to a particular one ofthe PSAPs via the dedicated emergency network; wherein the steps ofdetermining and storing are executed in the absence of an emergency callplaced by the particular communication device.
 2. The method defined inclaim 1, wherein the database is local to the packet switch.
 3. Themethod defined in claim 1, wherein the database is within the packetswitch.
 4. The method defined in claim 1, wherein determining a routingkey corresponding to the particular directory number comprises:determining the identity of an emergency zone corresponding to theparticular directory number; determining the routing key correspondingto the particular directory number on the basis of the emergency zonecorresponding to the particular directory number.
 5. The method definedin claim 4, further comprising: receiving a geographic location for theparticular directory number; validating the geographic location beforedetermining the emergency zone corresponding to the particular directorynumber.
 6. The method defined in claim 4, wherein determining theidentity of an emergency zone corresponding to the particular directorynumber comprises: receiving a geographic location for the particulardirectory number; determining the emergency zone corresponding to theparticular directory number on the basis of the received geographiclocation.
 7. The method defined in claim 6, further comprisingvalidating the geographic location before determining the emergency zonecorresponding to the particular directory number on the basis of thereceived geographic location.
 8. The method defined in claim 7, whereinthe geographic location comprises a street address.
 9. The methoddefined in claim 8, wherein validating the geographic location comprisesproviding the street address to a street address guide (SAG) andreceiving from the SAG an indication of whether the geographic locationis valid.
 10. The method defined in claim 6, wherein the geographiclocation comprises a postal code or a zip code, and wherein determiningthe emergency zone corresponding to the particular directory on thebasis of the received geographic location comprises consulting a tablethat maps postal codes or zip codes to emergency zones.
 11. The methoddefined in claim 7, wherein determining the identity of an emergencyzone corresponding to the particular directory number on the basis ofthe received geographic location comprises providing the validatedgeographic location to a 9-1-1 database management system and receivingfrom the 9-1-1 database management system the identity of the emergencyzone corresponding to the particular directory number.
 12. The methoddefined in claim 11, further comprising updating an automatic locationidentification (ALI) database with the particular directory number andwith the validated geographic location for the particular directorynumber.
 13. The method defined in claim 7, further comprising updatingan automatic location identification (ALI) database with the particulardirectory number and with the validated geographic location for theparticular directory number.
 14. The method defined in claim 13, whereinthe step of updating the ALI database is executed in the absence of anemergency call placed by the particular communication device.
 15. Themethod defined in claim 4, wherein determining a routing keycorresponding to the particular directory number comprises consulting acall routing list which maps emergency zones to routing keys.
 16. Themethod defined in claim 1, wherein the packet switch is connected to thededicated emergency network via at least one switching entity thatutilizes a respective forwarding table, the method further comprising:determining a set of emergency telephone numbers corresponding to theparticular directory number; entering the set of emergency numbers intothe forwarding table utilized by a switching entity that is connected tothe PSAP reached via the route defined by the routing key correspondingto the particular directory number.
 17. A computer readable storagemedium containing a program element for execution by a computing deviceto implement a method of enabling the delivery of emergency services tousers of a set of communication devices in a packet-switched network,each of the communication devices being associated with a respectivedirectory number, the method comprising: determining a routing keycorresponding to a particular directory number that is associated with aparticular communication device; and storing the particular directorynumber and the corresponding routing key in a database accessible to apacket switch in the packet-switched network, wherein the packet switchis connected to a plurality of public safety answering points (PSAPs)via a dedicated emergency network and wherein the routing keycorresponding to the particular directory number defines a route to aparticular one of the PSAPs via the dedicated emergency network; whereinthe steps of determining and storing are executed in the absence of anemergency call placed by the particular communication device.
 18. Amethod of enabling the delivery of emergency services to users of a setof communication devices in a packet-switched network, each of thecommunication devices being associated with a respective directorynumber, the method comprising: determining a routing key correspondingto a particular directory number that is associated with a particularcommunication device; and storing the particular directory number andthe corresponding routing key in a database local to a packet switch inthe packet-switched network; wherein the packet switch is connected to aplurality of public safety answering points (PSAPs) via a dedicatedemergency network; and wherein the routing key corresponding to theparticular directory number defines a route to a particular one of thePSAPs via the dedicated emergency network.
 19. The method defined inclaim 18, performed at the packet switch.
 20. The method defined inclaim 18, performed at a registration entity outside the packet switch.21. The method defined in claim 18, wherein the step of determining arouting key corresponding to the particular directory number isperformed at the packet switch.
 22. The method defined in claim 18,wherein determining a routing key corresponding to the particulardirectory number comprises: determining the identity of an emergencyzone corresponding to the particular directory number; determining therouting key corresponding to the particular directory number on thebasis of the emergency zone corresponding to the particular directorynumber.
 23. The method defined in claim 22, wherein the step ofdetermining the identity of an emergency zone corresponding to theparticular directory number is performed at the packet switch.
 24. Themethod defined in claim 23, wherein the step of determining the routingkey corresponding to the particular directory number on the basis of theemergency zone corresponding to the particular directory number isperformed at the packet switch.
 25. The method defined in claim 22,wherein the step of determining the identity of an emergency zonecorresponding to the particular directory number is performed at aregistration entity outside the packet switch.
 26. The method defined inclaim 25, wherein the step of determining the routing key correspondingto the particular directory number on the basis of the emergency zonecorresponding to the particular directory number is performed at theregistration entity.
 27. The method defined in claim 22, furthercomprising: receiving a geographic location for the particular directorynumber; validating the geographic location before determining theemergency zone corresponding to the particular directory number.
 28. Themethod defined in claim 22, wherein determining the identity of anemergency zone corresponding to the particular directory numbercomprises: receiving a geographic location for the particular directorynumber; determining the emergency zone corresponding to the particulardirectory number on the basis of the received geographic location. 29.The method defined in claim 28, further comprising validating thegeographic location before determining the emergency zone correspondingto the particular directory number on the basis of the receivedgeographic location.
 30. The method defined in claim 29, wherein thegeographic location comprises a street address.
 31. The method definedin claim 30, wherein validating the geographic location comprisesproviding the street address to a street address guide (SAG) andreceiving from the SAG an indication of whether the geographic locationis valid.
 32. The method defined in claim 28, wherein the geographiclocation comprises a postal code or a zip code, and wherein determiningthe emergency zone corresponding to the particular directory number onthe basis of the received geographic location comprises consulting atable that maps postal codes or zip codes to emergency zones.
 33. Themethod defined in claim 29, wherein determining the identity of anemergency zone corresponding to the particular directory number on thebasis of the received geographic location comprises providing thevalidated geographic location to a 9-1-1 database management system andreceiving from the 9-1-1 database management system the identity of theemergency zone corresponding to the particular directory number.
 34. Themethod defined in claim 33, further comprising updating an automaticlocation identification (ALI) database with the particular directorynumber and with the validated geographic location for the particulardirectory number.
 35. The method defined in claim 29, further comprisingupdating an automatic location identification (ALI) database with theparticular directory number and with the validated geographic locationfor the particular directory number.
 36. The method defined in claim 35,wherein the step of updating the ALI database is executed in the absenceof an emergency call placed by the particular communication device. 37.The method defined in claim 22, wherein determining a routing keycorresponding to the particular directory number comprises consulting acall routing list which maps emergency zones to routing keys.
 38. Themethod defined in claim 18, wherein the packet switch is connected tothe dedicated emergency network via at least one switching entity thatutilizes a respective forwarding table, the method further comprising:determining a set of emergency telephone numbers corresponding to theparticular directory number; entering the set of emergency numbers intothe forwarding table utilized by a switching entity that is connected tothe PSAP reached via the route defined by the routing key correspondingto the particular directory number.
 39. A computer readable storagemedium containing a program element for execution by a computing deviceto implement a method of enabling the delivery of emergency services tousers of a set of communication devices in a packet-switched network,each of the communication devices being associated with a respectivedirectory number, the method comprising: determining a routing keycorresponding to the particular directory number that is associated witha particular communication device; and storing the particular directorynumber and the corresponding routing key in a database local to a packetswitch in the packet-switched network; wherein the packet switch isconnected to a plurality of public safety answering points (PSAPs) via adedicated emergency network; and wherein the routing key correspondingto the particular directory number defines a route to a particular oneof the PSAPs via the dedicated emergency network.
 40. A method ofenabling the delivery of emergency services to users of a set ofcommunication devices in a packet-switched network, each of thecommunication devices being associated with a respective directorynumber, the method comprising: determining the identity of an emergencyzone corresponding to a particular directory number that is associatedwith a particular communication device; providing the particulardirectory number and the identity of the corresponding emergency zone toa packet switch in the packet-switched network, wherein the packetswitch is connected to a plurality of public safety answering points(PSAPs) via a dedicated emergency network; at the packet switch, and onthe basis of the identity of the corresponding emergency zone,determining a routing key corresponding to the particular directorynumber, wherein the routing key corresponding to the particulardirectory number defines a route to a particular one of the PSAPs viathe dedicated emergency network.
 41. The method defined in claim 40,further comprising: receiving a geographic location for the particulardirectory number; validating the geographic location before determiningthe emergency zone corresponding to the particular directory number. 42.The method defined in claim 40, wherein determining the identity of anemergency zone corresponding to the particular directory numbercomprises: receiving a geographic location for the particular directorynumber; determining the emergency zone corresponding to the particulardirectory number on the basis of the received geographic location. 43.The method defined in claim 42, further comprising validating thegeographic location before determining the emergency zone correspondingto the particular directory number on the basis of the receivedgeographic location.
 44. The method defined in claim 43, wherein thegeographic location comprises a street address.
 45. The method definedin claim 44, wherein validating the geographic location comprisesproviding the street address to a street address guide (SAG) andreceiving from the SAG an indication of whether the geographic locationis valid.
 46. The method defined in claim 42, wherein the geographiclocation comprises a postal code or a zip code, and wherein determiningthe emergency zone corresponding to the particular directory number onthe basis of the received geographic location comprises consulting atable that maps postal codes or zip codes to emergency zones.
 47. Themethod defined in claim 43, wherein determining the identity of anemergency zone corresponding to the particular directory number on thebasis of the received geographic location comprises providing thevalidated geographic location to a 9-1-1 database management system andreceiving from the 9-1-1 database management system the identity of theemergency zone corresponding to the particular directory number.
 48. Themethod defined in claim 47, further comprising updating an automaticlocation identification (ALI) database with the directory numberassociated with the particular communication device and with thevalidated geographic location for the particular directory number. 49.The method defined in claim 43, further comprising updating an automaticlocation identification (ALI) database with the particular directorynumber and with the validated geographic location for the particulardirectory number.
 50. The method defined in claim 49, wherein the stepof updating the ALI database is executed in the absence of an emergencycall placed by the particular communication device.
 51. The methoddefined in claim 40, wherein the packet switch is connected to thededicated emergency network via at least one switching entity thatutilizes a respective forwarding table, the method further comprising:determining a set of emergency telephone numbers corresponding to theparticular directory; entering the set of emergency numbers into theforwarding table utilized by a switching entity that is connected to thePSAP reached via the route defined by the routing key corresponding tothe particular directory number.
 52. The method defined in claim 40,wherein determining a routing key corresponding to the particulardirectory number comprises consulting a call routing list which mapsemergency zones to routing keys.
 53. The method defined in claim 40,further comprising storing the particular directory number and thecorresponding routing key in a memory local to the packet switch. 54.The method defined in claim 40, further comprising storing theparticular directory number and the corresponding routing key in amemory within the packet switch.
 55. A computer readable storage mediumcontaining a program element for execution by a computing device toimplement a method of enabling the delivery of emergency services tousers of a set of communication devices in a packet-switched network,each of the communication devices being associated with a respectivedirectory number, the method comprising: determining the identity of anemergency zone corresponding to a particular directory number that isassociated with a particular communication device; providing theparticular directory number and the identity of the correspondingemergency zone to a packet switch in the packet-switched network,wherein the packet switch is connected to a plurality of public safetyanswering points (PSAPs) via a dedicated emergency network; at thepacket switch, and on the basis of the identity of the correspondingemergency zone, determining a routing key corresponding to theparticular directory number, wherein the routing key corresponding tothe particular directory number defines a route to a particular one ofthe PSAPs via the dedicated emergency network.
 56. A method of enablingthe delivery of emergency services to users of a set of communicationdevices in a packet-switched network, each of the communication devicesbeing associated with a respective directory number, the methodcomprising: determining a routing key corresponding to a particulardirectory number that is associated with a particular communicationdevice; and storing the particular directory number and the routing keycorresponding to the particular directory number in a databaseaccessible to a packet switch in the packet-switched network; whereinthe routing key corresponding to the particular directory number isindicative of routing instructions to be followed by the packet switchupon receipt of a future emergency call placed by the particularcommunication device.
 57. The method defined in claim 56, the routinginstructions being first routing instructions, wherein the packet switchis connected to a plurality of public safety answering points (PSAPs)via a dedicated emergency network, wherein the routing key correspondingto the particular directory number is further indicative of secondrouting instructions to be followed by entities in the dedicatedemergency network upon receipt of a future emergency call placed by theparticular communication device.
 58. The method defined in claim 57,further comprising: receiving a geographic location for the particulardirectory number; validating the geographic location before determiningthe emergency zone corresponding to the particular directory number. 59.The method defined in claim 57, wherein determining the identity of anemergency zone corresponding to the particular directory numbercomprises: receiving a geographic location for the particular directorynumber; determining the emergency zone corresponding to the particulardirectory number on the basis of the received geographic location. 60.The method defined in claim 59, further comprising validating thegeographic location before determining the emergency zone correspondingto the particular directory number on the basis of the receivedgeographic location.
 61. The method defined in claim 60, wherein thegeographic location comprises a street address.
 62. The method definedin claim 61, wherein validating the geographic location comprisesproviding the street address to a street address guide (SAG) andreceiving from the SAG an indication of whether the geographic locationis valid.
 63. The method defined in claim 60, wherein determining theidentity of an emergency zone corresponding to the particular directorynumber on the basis of the received geographic location comprisesproviding the validated geographic location to a 9-1-1 databasemanagement system and receiving from the 9-1-1 database managementsystem the identity of the emergency zone corresponding to theparticular directory number.
 64. The method defined in claim 63, furthercomprising updating an automatic location identification (ALI) databasewith the particular directory number and with the validated geographiclocation for the particular directory number.
 65. The method defined inclaim 60, further comprising updating an automatic locationidentification (ALI) database with the particular directory number andwith the validated geographic location for the particular directorynumber.
 66. The method defined in claim 65, wherein the step of updatingthe ALI database is executed in the absence of an emergency call placedby the particular communication device.
 67. The method defined in claim57, wherein determining a routing key corresponding to the particulardirectory number comprises consulting a call routing list which mapsemergency zones to routing keys.
 68. The method defined in claim 59,wherein the geographic location comprises a postal code or a zip code,and wherein determining the emergency zone corresponding to theparticular directory number on the basis of the received geographiclocation comprises consulting a table that maps postal codes or zipcodes to emergency zones.
 69. The method defined in claim 56, whereindetermining a routing key corresponding to the particular directorynumber comprises: determining the identity of an emergency zonecorresponding to the particular directory number; determining therouting key corresponding to the particular directory number on thebasis of the emergency zone corresponding to the particular directorynumber.
 70. The method defined in claim 56, wherein the packet switch isconnected to the dedicated emergency network via at least one switchingentity that utilizes a respective forwarding table, the method furthercomprising: determining a set of emergency telephone numberscorresponding to the particular directory number; entering the set ofemergency numbers into the forwarding table utilized by a switchingentity that is connected to the PSAP reached via the route defined bythe routing key corresponding to the particular directory number. 71.The method defined in claim 70, the routing instructions being firstrouting instructions, wherein the routing key corresponding to theparticular directory number is further indicative of second routinginstructions to be followed by the switching entity that is connected tothe PSAP reached via the route defined by the routing key correspondingto the particular directory number.
 72. A computer readable storagemedium containing a program element for execution by a computing deviceto implement a method of enabling the delivery of emergency services tousers of a set of communication devices in a packet-switched network,each of the communication devices being associated with a respectivedirectory number, the method comprising: determining a routing keycorresponding to a particular directory number that is associated with aparticular communication device; and storing the particular directorynumber and the routing key corresponding to the particular directorynumber in a database accessible to a packet switch in thepacket-switched network; wherein the routing key corresponding to theparticular directory number is indicative of routing instructions to befollowed by the packet switch upon receipt of a future emergency callplaced by the particular communication device.
 73. A registration entityfor enabling the delivery of emergency services to users of a set ofcommunication devices in a packet-switched network, each of thecommunication devices being associated with a respective directorynumber, the registration entity comprising: a control entity; an I/O forcommunicating with a packet switch in the packet-switched network,wherein the packet switch is connected to a plurality of public safetyanswering points (PSAPs) via a dedicated emergency network; the controlentity being operative to execute the steps of: determining a routingkey corresponding to a particular directory number that is associatedwith a particular communication device, wherein the routing keycorresponding to the particular directory number defines a route to aparticular one of the PSAPs via the dedicated emergency network; andstoring the particular directory number and the routing keycorresponding to the particular directory number in a databaseaccessible to the packet switch; the steps of determining and storingbeing executed for the particular communication device in the absence ofan emergency call placed by the particular communication device.
 74. Anetwork entity for enabling the delivery of emergency services to usersof a set of communication devices in a packet-switched network, each ofthe communication devices being associated with a respective directorynumber, the network entity comprising: a control entity; an I/O incommunication with the control entity; the control entity beingoperative to execute the steps of: determining a routing keycorresponding to a particular directory number that is associated with aparticular communication device; and storing the particular directorynumber and the corresponding routing key in a database local to a packetswitch in the packet-switched network; wherein the packet switch isconnected to a plurality of public safety answering points (PSAPs) via adedicated emergency network; and wherein the routing key correspondingto the particular directory number defines a route to a particular oneof the PSAPs via the dedicated emergency network.
 75. The network entityof claim 74 being a registration entity.
 76. The network entity of claim74 being a packet switch.
 77. A packet switch for enabling the deliveryof emergency services to users of a set of communication devices in apacket-switched network, each of the communication devices beingassociated with a respective directory number, the packet switchcomprising: a control entity; an I/O in communication with the controlentity; the control entity being operative to execute the steps of:determining a routing key corresponding to a particular directory numberthat is associated with a particular communication device; and storingthe particular directory number and the routing key corresponding to theparticular directory number in a database; wherein the routing keycorresponding to the particular directory number is indicative ofrouting instructions to be followed by the packet switch upon receipt ofa future emergency call placed by the particular communication device.78. A computer-readable storage medium for storing data for access by anapplication program being executed at a packet switch in apacket-switched network, the memory comprising: a plurality of records,each record identifying: a directory number associated with a respectivecommunication device in the packet-switched network; and a routing keycorresponding to the directory number; wherein the routing keycorresponding to a particular directory number is indicative of routinginstructions to be followed by the packet switch upon receipt of afuture emergency call placed by the communication device associated withthe particular directory number.
 79. The computer-readable storagemedium defined in claim 78, each record further identifying an emergencyzone corresponding to the particular directory number.